A double-sided pressure-sensitive adhesive tape or sheet having at least a bubble-containing pressure-sensitive adhesive layer (also referred to as “bubble-containing double-sided pressure-sensitive adhesive tape”) has already been in use, and, as an example thereof, a double-sided pressure-sensitive adhesive tape or sheet having a bubble-containing acrylic pressure-sensitive adhesive layer (so-called “acryl foam double-sided pressure-sensitive adhesive tape or sheet) is already known. The bubble-containing double-sided pressure-sensitive adhesive tape, due to bubbles contained in the pressure-sensitive adhesive layer, can exhibit various characteristics different from those of the ordinary double-sided pressure-sensitive adhesive tape or sheet (double-sided adhesive tape or sheet) (see Patent Reference 1).
General structures of the bubble-containing double-sided pressure-sensitive adhesive tape include two constructions, namely a single separator type which utilizes a single releasable liner subjected to releasing treatments on both sides of a base material and in which both pressure-sensitive adhesive surfaces are protected by such single releasable liner in a state wound into a roll, and a double separator type which utilizes two releasable liners each subjected to a releasing treatment on one side of a base material and in which pressure-sensitive adhesive surfaces are protected respectively by the two releasable liners. In the bubble-containing double-sided pressure-sensitive adhesive tape in either construction, in order to prevent so-called “premature separation” phenomenon, the releasing treatment agents (releasing agents) for forming the releasably treated layers of the releasable liner for protecting the pressure-sensitive adhesive surfaces have to be so selected as to generate a difference between the peel strengths on the respective pressure-sensitive adhesive surfaces.
The “premature separation” phenomenon means, in a double-sided pressure-sensitive adhesive tape or sheet (also called “double-sided pressure-sensitive adhesive tape”) a situation where the releasable liner protecting the pressure-sensitive adhesive surface is not peeled off at an intended interface but causes a peeling at an interface that should remain adhered (Attached) to the pressure-sensitive adhesive surface. More specifically, it means, in the case of a double-sided pressure-sensitive adhesive tape and in peeling off the releasable liner or in rewinding a required amount from a double-sided pressure-sensitive adhesive tape wound in a roll, a phenomenon that the double-sided pressure-sensitive adhesive tape is peeled at an interface between the releasable liner and the pressure-sensitive adhesive surface which should remain adhered.
In particular, the releasably treated layer at a side having a larger peel strength from the pressure-sensitive adhesive surface (also called “heavier releasing-side releasably treated layer”) is required to have a peel strength higher than that in the releasably treated layer at a side having a smaller peel strength from the pressure-sensitive adhesive surface (also called “lighter releasing-side releasably treated layer”), and not to have an unnecessarily high peel strength. When the peel strength of the heavier releasing-side releasably treated layer from the pressure-sensitive adhesive surface is close to the peel strength of the lighter releasing-side releasably treated layer from the pressure-sensitive adhesive surface, it is liable to cause so-called “premature separation” phenomenon. Thus, when the releasable liner is peeled off from the double-sided pressure-sensitive adhesive tape, the tape itself causes damages such as creases or entanglements and becomes practically unusable. On the other hand, when the peel strength of the heavier releasing-side releasably treated layer from the pressure-sensitive adhesive surface becomes high, it may become difficult to peel off the releasable liner from the double-sided pressure-sensitive adhesive tape or, in peeling off the releasable liner, the double-sided pressure-sensitive adhesive tape itself which is adhered by the other pressure-sensitive adhesive surface to another article may be peeled off from such article, thereby resulting deteriorations in the working property or in the working efficiency.
In the ordinary double-sided pressure-sensitive adhesive tapes, it has been tried to cope with such detriments by employing a silicone type releasing agent, particularly a thermally curable silicone type releasing agent, as the releasing treatment agent for forming the heavier releasing-side releasably treated layer in the releasable liner.
Patent Reference 1: JP-A-2005-179561